For many years, photographic slide projectors have included a photographic slide handling mechanism, an optical system, a light source such as a tungsten filament lamp, a cooling fan and suitable controls for the lamp and slide changing mechanism. Such photographic slide projectors are commonly used for projecting 35 mm and 2 .times. 2 slides and are seriously light power limited for many applications. This limitation occurs because of the maximum light power which can be achieved from an internal tungsten filament lamp. Additionally, the photographic slide projector commonly displays a single transparency for 5 seconds to several minutes and despite light absorbing optics, there is a real danger of thermal damage to the photographic slide if a high intensity lamp is located in close proximity to the slide. Typically, a blower cooler has been included in such projectors to cool the lamp and the slide. Employing all of these approaches, the photographic slide projector is still capable of in the order 2,000 lumens output employing a conventional tungsten lamp with a total expected bulb life of in the order of 25 hours. With the power consumption and particularly short life of tungsten lamps, the operating costs of a typical configuration run in the order of $0.25 to $1.00 per hour.
High intensity lamp sources have heretofore been available for motion picture projectors and other applications where the lamps are installed, operated and serviced by professional personnel who are familiar with and able to take the necessary safety precautions with respect to the danger of lamp explosion in high pressure gas filled lamps. Since the photographic slide projector is more often used by amateurs or untrained individuals and youngsters of high school age, the use of high pressure gas filled lamps has not been possible. Such persons are not to be subjected to the risk of lamp explosion nor are they necessarily capable of focusing or positioning such lamps to obtain the optimum light output. Although high intensity gas filled lamps give a significantly greater light output than the tungsten lamp, they require enhanced cooling incompatible with existing slide projector housings.
Prior art patents disclosing various types of lamp assemblies are U.S. Pat. Nos. 3,639,751, 3,703,635, 3,720,822, and 3,766,377. U.S. Pat. No. 1,966,303 shows a light sensing mechanism.